Question

You ____ the examination again since you had already passed it.

A. needn't have taken
B. didn't need to take
C. needn't take
D. mustn't take
1. mustn't 表示强烈的禁止，不符合情景，D错误。
2. need have +过去分词表示过去需要做某事却未做，否定式表示过去不需要做某事却做了；这种用法含有责备的意味；need在这里为情态动词。比如：You needn't have taken the examination again since you have already passed it.这个句子是没有异议的；讲话者基于当前立场说出这番话。牛津词典并未指出本用法适用于何时的立场。
“⑧ (MODAL) (与否定词连用)本来不必，本来不需要 If someone needn't have done something, it was not necessary or useful for them to do it, although they did it.
● She could have made the sandwich herself; her mum needn't have bothered to do anything.
她本来可以自己做三明治的;她妈妈原本不必费心做任何事情。
● I was a little nervous when I announced my engagement to Grace, but I needn't have worried...
我宣布和格雷丝订婚时有点紧张，但我本不必担心的。”本段解释摘自于柯林斯词典。
然而柯林斯词典中同样并未指出“ it was not necessary”应用于当前的立场还是过去某个时间的立场。
“ She could have made the sandwich herself; her mum needn't have bothered to do anything.”could have made表示对过去的推测，意思是“她以前可能自己会做三明治”，是讲话者基于当前立场指出的，“her mum needn't have bothered to do anything”和前半句之间的分号表并前、后半句为并列关系，所以我认为后半句应当同样基于当前立场。
因此，我认为 need have+过去分词只适用于讲话者基于当前立场提出的观点。而题目中后半句用了“ had already passed it”，显然是基于通过考试与讲话之间的某个时间，属于旧事重提。假设被指责的人（甲）一周前通过了考试，前天他又参加了同样的考试，讲话的人是甲的妈妈（乙）；昨天乙发现甲参加了已经通过的同样的考试科目，昨天乙会说“You needn't have taken the examination again since you have already passed it.”，今天乙又想起了这件令自己不满的事情，于是说“You ____ the examination again since you had already passed it.”用以重新提起昨天指责的情景，即家长没完没了的唠叨。A错误。
needn't take中need同样为情态动词，
3. “⑤ (MODAL) (与否定词连用)不必，没有必要 If you tell someone that they needn't do something, or that something needn't happen, you are telling them that that thing is not necessary, in order to make them feel better.
● You needn't worry...
你不必担心。
● This needn't take long, Simon...
西蒙，这花不了多长时间。”摘自于柯林斯词典。
同样的，词典中并未指明是否可以将 needn't用于过去的时间段，但是例句中只应用于当前。
4. 这道选择题的答案是B，应该是国人造句。如果这句话的表达方式、答案都正确，说明“needn't have +过去分词”、“needn't”这两种need作为情态动词的用法只适用于基于当前的意见。

以上2、3条分析都是以本题目表达方式正确为前提，因为牛津词典、柯林斯词典都没有明确指出need作为情态动词的这两种用法能否适用于基于过去的意见。
最终意见：我觉得这个句子是中国式英语。如果有人认识亚历山大，请带我向他本人请教这个问题。

Answer 1

正确的答案选B，释义为：你不必再参加考试，因为你已经通过了